I tend to stay at the Hilton, but have stayed at the Marriott as well, both are decent. If you go directly on to the hotel website, they normally have some packages available (depending on what interests you, dining, gambling, wine tastings etc.) and have falls view rooms. The fireworks only happen on Friday nights in January, but they are illuminated every night (not a show per say, just lights all evening).
I do not believe the Hornblower runs in the winter months, too much ice in the river.
I do like the falls in winter, but it can be very very cold down at the waters edge at time, and slippy, so be careful and pack some warm clothes, hats, gloves, and winter boots.